course Phy231
2/7/10 7:30pm
If the velocity of the object changes from 3 cm / sec to 11 cm / sec in 9 seconds, then at what average rate is the velocity changing?11cm/sec - 3cm/sec= 8cm/sec 9sec/ cm/sec= 1.125 cm/sec/sec
You've divided `dt by `ds, which would be the average rate at which clock time is changing with respect to velocity.
A ball rolling from rest down a constant incline requires 8.6 seconds to roll the 68 centimeter length of the incline.
What is its average velocity? 68cm/8.6sec= 7.9cm/sec
An object which accelerates uniformly from rest will attain a final velocity which is double its average velocity.
What therefore is the final velocity of this ball? 7.9cm/sec*2= 15.8cm/sec
What average rate is the velocity of the ball therefore changing? 15.8/sec -0cm/sec(which is rest)=15.8cm/sec 15.8cm/sec/8.6sec=1.84 cm/sec/sec
An automobile accelerates uniformly down a constant incline, starting from rest. It requires 15 seconds to cover a distance of 172 meters. At what average rate is the velocity of the automobile therefore changing?
172meters/15sec=11.47m/sec is avg velocity therefore 11.47m/sec*2=22.93m/sec is the final velocity
so, 22.93m/sec/15sec=1.53m/sec/sec is the average rate at which the velocity changes
Very good, but be sure you see your error on the first question.